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Title: Denitrification and nitrous oxide cycling within the upper oxycline of the eastern tropical South Pacific oxygen minimum zone
Authors: Laura Farías
Maribeb Castro-González
Marcela Cornejo
José Charpentier
Juan Faúndez
Narin Boontanon
Naohiro Yoshida
University of Concepcion
Tokyo Institute of Technology
Universidad de Tolima
Faculty of Environment and Resource Studies, Mahidol University
Keywords: Agricultural and Biological Sciences;Earth and Planetary Sciences
Issue Date: 1-Jan-2009
Citation: Limnology and Oceanography. Vol.54, No.1 (2009), 132-144
Abstract: One of the shallowest, most intense oxygen minimum zones (OMZs) is found in the eastern tropical South Pacific, off northern Chile and southern Peru. It has a strong oxygen gradient (upper oxycline) and high N2O accumulation. N2O cycling by heterotrophic denitrification along the upper oxycline was studied by measuring N2O production and consumption rates using an improved acetylene blockage method. Dissolved N2O and its isotope (15N:14N ratio in N2O or δ15N) and isotopomer composition (intramolecular distribution of15N in the N2O or δ15Nαand δ15Nβ), dissolved O2, nutrients, and other oceanographic variables were also measured. Strong N2O accumulation (up to 86 nmol L-1) was observed in the upper oxycline followed by a decline (around 8-12 nmol L-1) toward the OMZ core. N2O production rates by denitrification (NO2-reduction to N2O) were 2.25 to 50.0 nmol L-1d-1, whereas N2O consumption rates (N2O reduction to N2) were 2.73 and 70.8 nmol L-1d-1. δ15N in N2O increased from 8.57%‰ in the middle oxycline (50-m depth) to 14.87%‰ toward the OMZ core (100-m depth), indicating the progressive use of N2O as an electron acceptor by denitrifying organisms. Isotopomer signals of N2O (δ15Nαand δ15Nβ) showed an abrupt change at the middle oxycline, indicating different mechanisms of N2O production and consumption in this layer. Thus, partial denitrification along with aerobic ammonium oxidation appears to be responsible for N2O accumulation in the upper oxycline, where O2levels fluctuate widely; N2O reduction, on the other hand, is an important pathway for N2production. As a result, the proportion of N2O consumption relative to its production increased as O2decreased toward the OMZ core. A N2O mass balance in the subsurface layer indicates that only a small amount of the gas could be effluxed into the atmosphere (12.7-30.7 μmol m-2d-1) and that most N2O is used as an electron acceptor during denitrification (107-168 μmol m-2d-1). © 2009, by the American Society of Limnology and Oceanography, Inc.
ISSN: 00243590
Appears in Collections:Scopus 2006-2010

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